Why is the liquid's reflection look so weird after the render? (Blender Guru tutorial)
It looks like your liquid mesh is intersecting very slightly with the cup.  It's possible they have different render values for their Subdivision Surface modifiers, or a common fix (and one given by Price) you could try is scaling the liquid mesh up very slightly.
This intersects the liquid's outer faces into the glass completely which gets you a pretty good render.
Additionally, there are several posts on this site and others regarding the proper physically correct method of rendering liquids in glasses, which I will link here.
Liquid / glass interface IOR and normals in Cycles - BSE
fluid in a glass - BSE
Fluid in a Glass - Greg Zaal's blog